Cigarette lighter with improved safety properties

ABSTRACT

A cigarette lighter with improved safety property includes a combustion chamber formed as a receptacle in which a cigarette to be lit is inserted. The receptacle is formed of three concentric vented tubes. The combustion chamber is shaped and dimensioned in a manner to completely envelop the flame produced in the combustion chamber, and to prevent any objects with dimensions larger than diameter of a cigarette to be received in the combustion chamber. A flame stabilizer is secured in the inner tube of the receptacle unit at a predetermined distance from the burner in order to limit the insertion of the cigarette and to prevent the unwanted extinction of the flame if the cigarette is inserted too close to the source of the flame.

REFERENCE TO RELATED APPLICATIONS

This Utility Patent Application is based on Provisional Patent Application No. 60/592,876 filed Jul. 30, 2004.

FIELD OF THE INVENTION

The present invention relates to cigarette lighters and more in particular, to systems for improving fire safety considerations of cigarette lighters.

In overall concept, the present invention relates to a cigarette lighter which generates a flame completely enveloped within the combustion chamber of the cigarette lighter, whereby the cigarette being lit is brought into contact with the flame within the combustion chamber.

Further, the present invention relates to a cigarette lighter equipped with a receptacle designed according to the geometry of a cigarette such that only objects of similar geometry or smaller than a cigarette may be inserted into the receptacle. In this manner, the cigarette lighter provides local heating to the cigarette, and as the result, reduced heating to objects surrounding the cigarette lighter.

The present invention further relates to a cigarette lighter which includes an elongated combustion chamber receiving the cigarette to be ignited, which includes a plurality of concentric stainless steel tubes designed to improve the flame characteristics, temperature distribution, as well as ignition propensity of the cigarette lighter.

Still further, the present invention relates to a cigarette lighter having a flame recession acting as a medium to absorb energy from the flame within the recession while increasing the distance between the flame source and the exit of the hot gases. The flame recession completely contains the flame, thus making it less enticing to curious children, and further significantly improves exit gas properties.

BACKGROUND OF THE INVENTION

Small flames, such as those found in candles, matches, cigarette/utility lighters and the incipient fire pose a significant fire hazard. These small flames can release enough thermal energy to cause unwanted ignition and sustain burning. Small ignition sources are dangerous and may produce a fire that may remain unnoticed for a significant period of time. Of these small sources, candles are most commonly recognized as fire hazards. The National Fire Protection Association (NFPA) recognizes this risk and has published a fact sheet with safety tips for using candles in the home. Other small ignition sources include matches and cigarette lighters. Cigarette lighter flames produce a high risk of ignition and therefore need special consideration.

The current standard for improving safety of lighters focuses on adding mechanical child safety features to lighters. These additional mechanical child safety features however do nothing to resolve the unwanted ignition propensity of the lighter flame.

Existing mechanical safety features provided for cigarette lighters are cumbersome and are often bypassed in order to improve ease of use. These “child safety” features are intended to inhibit use of the lighter by persons who lack the motor skills and understanding to operate the lighter. Studies conducted by the National Association of State Fire Marshals (NASFM), such as the Juvenile Firesetter Program, have shown that these features are insufficient for reducing unwanted ignition by juveniles ages 4 to 16. Additionally, the American Society for Testing and Materials (ASTM) standard for regulation of cigarette lighters, ASTM F400-00, is qualitative in nature with respect to unwanted ignition propensity and does not characterize the increased hazard of many new cigarette lighter designs. The NASFM has recognized that there is a need for detailed thermal characterization of cigarette lighters in order to determine the ignition propensity and methods for reducing the ignition propensity.

There is very little previous work characterizing the ignition hazard from cigarette lighters. However, previous work on the thermal behavior of fire plumes may be applied to cigarette lighters with appropriate scaling. Some studies have characterized the gas temperature above a fire source, heat transfer to surfaces above a fire source, ignition of materials with external heating, and transition to turbulence in plumes.

Temperature profiles are a key thermal characteristic of fire flows as they are indicative of the heating potential of the flow. Lighter nozzles that produce higher plume temperatures correspondingly have a higher risk of ignition than those with lower temperatures assuming comparable velocities. Morton et al. previously determined the centerline velocity and temperature distributions in a turbulent plume issuing from a point source (Morton B. R., et al., “Turbulent Gravitational Convection from Maintained and Instantaneous Sources”, Proceedings of the Royal Society of London, Series A, V. 234, pp. 1-23, 1956). Morton, et al. found that the centerline temperature decay along the plume axis followed a (−5/3) power law: $\begin{matrix} {\frac{T - T_{\infty}}{T_{\infty}} = {\frac{5Q}{6\alpha}\left( {\frac{9}{10}\alpha\quad Q} \right)^{{- 1}/3}z^{{- 5}/3}}} & (1) \end{matrix}$ where T is the centerline plume temperature, T_(∞) is the ambient temperature, Q is the energy release rate of the flame, α is the plume entrainment coefficient constant experimentally found to be 0.11, and z is the characteristic height above the source, based on integral analysis of the turbulent plume equations.

McCaffrey, et al. measured the centerline temperature decay along the plume axis above fire sources (McCafrrey, B. T., et al., “Purely Buoyant Diffusion Flames: Some Experimental Results”, Center for Fire Research, National Engineering Laboratory, National Bureau of Standards, No. NBSIR 79-1910, 1979). McCaffrey, et al. found that the temperature decayed according to the same theoretical power law in the plume zone sufficiently far from the source. They also identified a flame zone with constant temperature and an intermittent zone where the temperature decayed inversely with position along the plume axis. Flows from cigarette lighter flames are rarely turbulent near the source. Thus it is important to observe the laminar characteristics and compare them to classical laminar theories for appropriate analysis. The laminar plume equations were solved by Fujii using similarity analysis (Fujii, T. I., “Theory of Steady Laminar Natural Convection Above a Horizontal Line Heat Source and a Point of Heat and Mass Transfer”, Vol. 6, pp. 597-606, 1963). Fujii's laminar analysis predicted that centerline temperatures should decay inversely with position above the plume. The flow generated by cigarette lighters can be considered a forced flow, especially in cases where the fuel is premixed with air. Morton, et al. has investigated plumes generated by a steady release of mass, momentum and buoyancy, analytically illustrating the difference between forced plumes and purely buoyant plumes. The results of this analysis shows that forced plumes decay similarly to a jet in the near field with (−1) power law decay and transitioning to plume decay in the far field with an offset.

Transition to turbulence has been studied extensively for vertical plumes. Determining if and where this turbulence occurs is of great importance to scaling data in the flows produced by cigarette lighter flames since the flow is initially laminar which eventually transitions to turbulent flow. Krishnamurthy et al. and Jiang et al. have studied buoyant flows adjacent to a vertical surface using experimental and modeling approaches respectively (Krishnamurthy, R., and Gebhart, B., “An Experimental Study of Transition to Turbulence in Vertical Mixed Convection Flows”, Journal of Heat Transfer, Vol. 111, pp. 121-130, 1989; and Jiang, X., and Luo, K. H., “Dynamics and Structure of Transitional Buoyant Jet Diffusion Flames with Side-Wall Effects”, Combustion and Flame, Vol. 133, pp. 29-45, 2003).

This geometry is of particular interest for convective heating of the side wall as the convective heating coefficient has a strong dependence on the level of turbulence. Bejan and Kimura et al. have studied free buoyant plumes, and provide a fundamental method for determining the transition to turbulence (Bejan, A., Convection Heat Transfer, Ch. 6, John Wiley and Sons, New York, pp. 202-223, 1983; and Kimura, S., and Bejan, A., “Mechanism for Transition to Turbulence in Buoyant Plume Flow”, International Journal of Heat and Mass Transfer, Vol. 26, pp. 1515-1532, 1983). Using the instability analysis prescribed by Kimura et al., a predictor of the transition to turbulence can be predicted by z_(t)˜Q^(−1/2), where z_(t) is the turbulent transition height and Q is the energy release rate of the flame. Similarly, a critical Rayleigh number approach, $\begin{matrix} {{{Ra}_{q} = {\frac{{gz}_{ir}^{2}\overset{.}{Q}}{({avk})_{air}T_{\infty}} \leq 10^{10}}},} & (2) \end{matrix}$ where g is the gravitational constant, z_(ir) is the height for transition to turbulence, and (avk)_(air) are the thermal diffusivity, kinematic viscosity, and conductivity of air respectively, can be used as described by Bejan.

Heat transfer to horizontal surfaces above large fire sources has also been studied extensively. This configuration has been used for studying heat loading on ceilings and other objects above fires. Heat transfer to a horizontal surface results from plume impingement and the formation of a wall jet traveling radially outward below the horizontal surface. In this study, heat flux was used as a metric for ignition propensity of the source. Alpert determined an analytical solution from integral analysis for ceiling jet temperatures, velocities, and jet thicknesses (Alpert, R. L., “Fire Induced Turbulent Ceiling Jet”, Factory Mutual Research Corporation, FMC 19722-2, 1971). He was able to determine a local heat flux to the ceiling from the theory that he developed for ceiling jets. He found a dimensionless heat flux: ξ=q″H ² /{dot over (Q)}  (3) where q″ is the incident heat flux, and H is the ceiling height, from his turbulent heat transfer analysis. Veldman et al. and Faeth et al. conducted experiments for ceiling jet heat transfer (Veldman, C. C., Kubota, T., and Zukoski, E. E., “An Experimental Investigation of the Heat Transfer from a Buoyant Gas Plume to a Horizontal Ceiling—Part 1. Unobstructed Ceiling”, Center for Fire Research, National Engineering Laboratory, National Bureau of Standards, No. NBS-GCR-77-97, 1975; and Faeth, G. M. and You, H. Z., “An Investigation of Fire Impingement on a Horizontal Ceiling”, Center for Fire Research, National Engineering Laboratory, National Bureau of Standards, No. NBS-GCR-81-304 (1981). They found significant scatter in the heat flux data with only limited agreement with the Alpert's ceiling jet theory. They attributed the scatter to other phenomena that may be important to the ceiling heat transfer including radiation effects.

Chow and Motevalli have performed numerical studies of the ceiling jet to characterize the velocity and temperature profile of the flow as a function of the radius (Chow, W. K., “Numerical Studies on the Transient Behaviour of a Fire Plume and Ceiling Jet”, Mathematical and Computer Modeling, Vol. 17, pp. 71-79, 1993; and Motevalli, V., “Numerical Prediction of Ceiling Jet Temperature Profiles During Ceiling Heating Using Empirical Velocity Profiles and Turbulent Continuity and Energy Equations”, Fire Safety Journal, Vol. 22, pp. 125-144, 1994). These profiles are useful for calculating heat flux to a ceiling surface, however, the studies do not evaluate the steady state solution for a thermally thin ceiling. Motevalli, et al. has investigated the small scale steady state case (Motevalli, V., and Marks, C. H., “Transient and Steady State Study of Small-Scale, Fire-Induced Unconfined Ceiling Jets”, 5^(th) AIAA/ASME Thermophysical and Heat Transfer Conferences, ed. Quintiere, J. G. and Cooper, L. Y., American Society of Mechanical Engineers, New York, pp. 49-61, 1990). This study illustrates that there is a negligible difference between the transient and the steady state ceiling jet flow however, it does not characterize heat transfer to the ceiling.

The ability of a cigarette lighter to ignite thin materials is of particular interest in determining the devices safety performance. Unfortunately, much of the ignition research conducted has focused on thermally thick or semi-infinite solids. Relatively little work has been done with thermally thin solids.

Drysdale has discussed the theory behind ignition of thermally thin slabs based on the solution of the differential one-dimensional heat conduction equation, showing that regardless of the mode of heat transfer, ignition time is directly proportional to the thermal capacity per unit area (τpc) where τ is the thickness, p is the density and c is the specific heat of the ignition material (Drysdale, D. D., An Introduction to Fire Dynamics, Second Edition, Ch. 6, John Wiley and Sons, New York, pp. 193-232, 1998).

Studies performed by Zhou, et al., Thomson, et al., Atreya, et al., and Moghtaderi, et al., discuss methods for determining critical heat fluxes and temperatures for ignition of various materials under several different heating conditions. These studies used piloted ignition and thermally thick materials (Zhou, Y. Y., Walther, D. C., and Fernandez-Pello, A. C., “Numerical Analysis of Piloted Ignition of Polymeric Materials”, Combustion and Flame, Vol. 131, pp. 147-158, 2002; Thomson, H. W., Drysdale, D. D., and Beyler, C. L., “An Experimental Evaluation of Critical Temperature as a Criterion for Piloted Ignition”, Fire Safety Journal, Vol. 13, pp. 185-196, 1988; Atreya, A., and Wichman, I. S., “Heat and Mass Transfer During Piloted Ignition of Cellulosic Solids”, Journal of Heat Transfer, Vol. 111, pp. 719-725, 1989; and Mohgtaderi, B., Novozhilov, V., Fletcher, D. F., and Kent, J. H., “A New Correlation for Bench-Scale Piloted Ignition Data of Wood”, Fire Safety Journal, Vol. 29, pp. 41-59, 1997).

Nelson, et al. performed a study of thermally thin solids in the cone calorimeter illustrating that the critical heat flux can be determined graphically by from 1/t_(ig) versus the incident heat flux, q″, where t_(ig) is the time to ignition (Nelson, M. I., Brindley, J., and McIntosh, A. C., “Ignition Properties of Thermally Thin Materials in the Cone Calorimeter: A Critical Mass Flux Model”, Combustion Science and Technology, Vols. 113-114, pp. 221-241, 1996).

Although extensive studies regarding the characterization of flames have been performed which are discussed in previous paragraphs, still further investigations have been found to be needed in order to design a cigarette lighter with satisfactory safety properties.

Commercial cigarette lighters are presented in FIGS. 1-3. Diffusion type lighter 10, illustrated in FIG. 1, is a commercial cigarette lighter using a standard port-type nozzle 12 used to produce a candle-like flame. In the diffusion lighter, the fuel is directly injected through an approximate 0.5 mm diameter opening from a fuel reservoir 14 into the ambient air where it begins to mix diffusely. The fuel is ignited using a spark that allows for a steady sustained burning of the fuel. The reaction zone only occurs at the fuel-air interface as determined by diffusion.

Shown further in FIG. 2, a “Premixed 1” type cigarette lighter 16 uses a Bunsen burner type nozzle 28 which is widely available at specialty stores and on-line. This nozzle produces a blue flame due to fuel-air mixing prior to combustion. The fuel is injected from the fuel reservoir 18 through an approximate 70 mm orifice 20 to produce a high velocity jet. This jet is injected through a vented chamber 22 where it entrains air prior to combustion. The fuel-air mixture is then injected into a small combustion chamber 24 of depth δ_(light)=6 mm, where it is ignited by a piezoelectric spark device. A simple wire mesh, or flame stabilizer 26, encloses the combustion chamber to provide limited stability of the flame in windy conditions. Some of the fuel reacts in the combustion chamber and the remainder of the unburned fuel and air pass through the flame stabilizer 26 prior to its combustion. As seen in FIG. 2, a portion of the flame exists outside of the chamber. Since the nozzle 28 produces a combustible fuel-air mixture, the reaction zone occurs evenly at all locations in the flame. This uniform combustion zone produces a blue flame since little soot is formed, reducing its luminocity.

A “Premixed 2” type lighter 30, shown in FIG. 3, also uses a Bunsen burner type. The “Premixed 2” lighter produces a blue flame due to fuel-air mixing prior to combustion. The fuel is injected through a 70 mm orifice 32 to produce a high velocity jet. This jet is injected through a vented chamber 34 where it entrains air prior to combustion, similar to “Premixed 1” type lighter 16. The fuel-air mixture is then injected into a small combustion chamber 36 having the depth δ_(light)=3 mm, where it is ignited by a piezoelectric spark device. This lighter 30 does not use a flame stabilizer as described in “Premixed 1”, and much of the combustion occurs external the chamber.

All three prior art lighters in FIGS. 1-3, have a generally high degree of hazardousness due to the fact that the flame either is generated external the cigarette lighter or extends beyond the lighter, thus making ambient items susceptible to the ignition.

Thus a need exists for cigarette lighters with improved ignition propensity and increased safety without adding mechanical child safety features thereto.

SUMMARY OF THE INVENTION

It is a major object of the present invention to provide a cigarette lighter which demonstrates improved ignition propensity and increased safety properties.

It is another object of the present invention to provide an improved design of the cigarette lighter based on characteristic parameters describing ignition propensity, including center line temperature profiles denoting transition to turbulence of the flame, heat flux profiles to a horizontal flat plate, and ignition of filter paper.

It is a further object of the present invention to provide a cigarette lighter having a combustion chamber sized to receive small objects similar to cigarettes wherein larger objects cannot be introduced into the combustion chamber.

It is also an object of the present invention to provide a cigarette lighter in which a generated flame is contained completely in the combustion chamber which envelops the flame. Since no flame extends outside the combustion chamber, the cigarette has to be introduced into the combustion chamber for contact with the produced flame and resultant ignition. The flame recession (combustion chamber) acts as a medium to absorb energy from the flame while increasing the distance between the flame source and the exit of the hot gases as well as significantly improving exit gas properties.

The present invention is directed to a cigarette lighter with improved safety properties, e.g., the diminished unwanted ignition propensity without adding mechanical child safety features. The cigarette lighter is designed based on extensive study and evaluation of characteristic parameters describing ignition propensity, including center line temperature profiles in view of transition to turbulence, heat flux profiles to a horizontal flat plate, and ignition of filter paper. The cigarette lighter includes a combustion chamber implemented as a receptacle unit (flame recession) dimensioned to completely envelop a flame existing in the combustion chamber. A cigarette has to be inserted in the receptacle unit in order to be brought in contact with the flame. It is an important feature of the receptacle unit of the cigarette lighter that an opening through which the cigarette is inserted into the receptacle unit is sized to be in the order of the diameter of the cigarette, such that only objects of the size of the cigarette or smaller may be introduced therein.

The receptacle unit is formed by three concentric tubes, particularly an inner tube, an outer tube, and a middle tube concentrically sandwiched between the inner and outer tubes. All three tubes are vented tubes and have a plurality of vent openings formed in the tube's walls which are arrayed in a predetermined fashion.

A flame stabilizer in the form of a mesh made of titanium wire is introduced in the inner tube a predetermined distance from the exit opening in order to limit the insertion of the cigarette into the combustion chamber to prevent unwanted extinction of the flame which can be caused by the cigarette being brought too close to the source of the flame.

The cigarette lighter, in addition to the combustion chamber, formed of three vented tubes, includes a burner nozzle positioned at the bottom of the combustion chamber for delivering a fuel-air mixture thereto, an ignition unit operatively coupled to the combustion chamber to ignite the fuel-air mixture to produce the flame, a fuel reservoir containing a fuel, an air-fuel mixing chamber coupled to the fuel reservoir through a fuel connection tube, and an operation button which upon actuation thereof activates the ignition unit. The ignition unit includes a piezoelectric spark device and a spark ignition wire extending into the combustion chamber. The air-fuel mixing chamber is coupled to the burner nozzle to inject the fuel-air mixture into the combustion chamber.

These, and other features and advantages of the present invention, will be fully understood from the following description of the present invention accompanied by the Drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the diffusion type cigarette lighter of the prior art with the flame plume formed and extending completely outside of the cigarette lighter;

FIG. 2 shows schematically a commercial “Premixed 1” type cigarette lighter of the prior art with the flame plume formed within the combustion chamber, but extending outside the cigarette lighter;

FIG. 3 illustrates schematically a commercial “Premixed 2” type cigarette lighter of the prior art where the flame extends outside the cigarette lighter;

FIG. 4 is a schematic representation of the cigarette lighter of the present invention having the flame contained completely in the cigarette lighter;

FIG. 5 is a cross-section of FIG. 4 taken along Lines 5-5 thereof illustrating a multi-tube arrangement of the combustion chamber of the cigarette lighter of the present invention;

FIGS. 6 and 7 illustrate alternative embodiments of the multi-tube arrangement of the receptacle unit of the cigarette lighter of the present invention;

FIG. 8 is a diagram showing in comparison central line temperatures of the cigarette lighter of the present invention and of diffusion, “Premixed 1”, and “Premixed 2” cigarette lighters of the prior art indicating that the temperature of the subject cigarette lighter near the exit plane is much lower than the temperature observed for the existing cigarette lighters;

FIG. 9 is a diagram of the dimensionless temperature vs. dimensionless height for the cigarette lighter of the present invention compared to the existing cigarette lighters (diffusion, “Premixed 1” and “Premixed 2”) indicating that turbulent plume behavior for the cigarette lighter of the present invention occurs at a height greater than for the existing cigarette lighters;

FIG. 10 is a diagram showing temperature fluctuations of the cigarette lighter of the present invention compared to the same of the existing cigarette lighters (diffusion, “Premixed 1”, and “Premixed 2”) vs. dimensionless height indicating a delayed turbulent transition for the cigarette lighter of the present invention;

FIGS. 11-13 are diagrams showing tube surface temperatures for the inner tube, middle tube, and the outer tube, respectively, of the receptacle unit of the cigarette lighter of the present invention;

FIG. 14 is a diagram showing a radial heat flux profile corresponding to the peak observed stagnation point of the heat flux for the cigarette lighter of the present invention compared to cigarette lighters of the prior art (diffusion, “Premixed 1”, and “Premixed 2”); and,

FIG. 15 is a diagram showing stagnation point heat fluxes vs. height for the cigarette lighter of the present invention compared to the cigarette lighters of the prior art (diffusion, “Premixed 1”, and “Premixed 2”) indicating significant improvement of the cigarette lighter of the present invention over prior art cigarette lighters.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 4, cigarette lighter 40 of the present invention includes a fuel reservoir 42 containing fuel. The fuel is delivered to an air mixing chamber 44 through the orifice 46. The fuel reservoir 42 is connected to the orifice 46 by a fuel connection tube 48. In the air mixing chamber 44, the fuel mixes with the air to form the air-fuel mixture which is delivered to a burner nozzle 50 and is injected therethrough into a combustion chamber 52.

A piezoelectric spark device 54 is operatively coupled to an operation button 56 for actuation/deactuation. Upon actuation, the piezoelectric spark device 54 generates a discharge which is delivered through a spark ignition wire 58 into the combustion chamber 52 filled with the fuel-air mixture. The discharge from the spark ignition wire 58 ignites the fuel-air mixture in the combustion chamber and produces a flame 60 therein.

The combustion chamber 52 consists of three concentric vented stainless steel tubes 62, 64, and 66 linked together using set screws which form a receptacle unit 68 receiving a cigarette 70 to be lit. The receptacle unit 68 also may be considered a flame recession which completely contains the flame.

The vented tubes 62-66 which are represented as an inner tube 62, middle tube 64, and the outer tube 66 in FIGS. 4 and 5, all have offset vents 72 (best shown in FIGS. 6 and 7). Circular vents are shown for illustration only, however, the vent contours may be of other contoured outlines. In one example, the vents have a diameter of 3.2 mm for the tubes 62 and 64, and a diameter 4.8 mm on the tube 66. The vents 72 may be spaced at 3.2 mm each from the other on the center thereof and at 60° intervals. The vents 72 reduce velocities of the fluxes within the tube for flame stabilization. If the tubes 62-66 were not vented, flame would propagate rapidly away from the point of ignition (which is close to the burner nozzle 50) rapidly expelling burning gases through the exit opening 82 at the end 74 of the tubes followed by flame extinction. By introducing vented tubes 62-66 with the offset vent 72 formed therein, the flame 60 speed has been reduced significantly resulting in a stable flame. Flame 60 is completely contained within the combustion chamber 52 leaving no visible combustion as illustrated in FIG. 4.

The inner tube 62 is designed to accommodate the outside diameter (8 mm) and length (83 mm) of a standard cigarette. The inner tube 62 acts as a heat sink that absorbs a portion of energy produced by the flame 60. In the cigarette lighter of the present invention, some of the energy released by the flame is conducted away by the steel tube and the remaining energy is convected away by the hot gases. This is in contrast to prior art cigarette lighters, where all of the energy released by the flame is convected away by the hot gases in the plume.

The underlining principle of the design of the subject cigarette lighter is that when the energy capacity of the hot gases is reduced, the ignition propensity of the hot gases is also reduced. The energy conducted away by the inner tube 62 is gradually released by natural convection and radiation to the outer two tubes (middle tube 64 and the outer tube 66). The three tube configuration was studied based on qualitative observations of surface temperature of the outer tube 66, as will be presented further herein. Two tube configurations have also been studied, and it was shown that the surface temperature of the outer of two tubes increased to the threshold of pain much more rapidly than in the three tube configuration.

The performance of the three tube configuration was studied (as will be presented further herein) using a model of a one-dimensional heat transfer with two zones for each tube. The lower zone is the region below a flame stabilizer 76, and the upper zone in the region above the flame stabilizer. The two zones communicate through a simple conduction assumption. Energy is transferred between the tubes 62, 64, and 66. The convection and radiation transfer has been calculated as described by Incropera (Incropera F. P., et al., “Fundamentals of Heat and Mass Transfer, 5^(th) Edition, John Wiley & Sons, New York, 2002). The surface temperatures of each tube have been calculated iteratively to simulate non-transient heat transfer.

The flame stabilizer 76 is introduced into the inner tube 62 and positioned a predetermined distance from the burner nozzle 50 (or from the exit opening 82) to limit the insertion of the cigarette 70 into the tube 62. This is done to prevent extinction of the flame 60 if the cigarette approaches too close to the burner nozzle 50.

The dimensions of the tubes 62-66 in one form of the system includes: tube 62 (inner tube): inside diameter—0.38 inches, outside diameter—0.5 inches; tube 64 (middle tube): inside diameter—0.63 inches, outside diameter—0.75 inches; and tube 66 (outer tube): inside diameter—0.87 inches, outside diameter—1 inch.

In the embodiment shown in FIG. 6, the integral outer tube 66 extends from the end 74 of the cigarette lighter 40 to the bottom of the reservoir 72. The length of such an outer tube 66 shown in FIG. 6 is approximately 4.75 inches. This tube has an upper portion provided with vents 72, below which the tube 66 has an opening for the actuation button 56 to protrude therethrough and serves merely as a holder and the casing for the reservoir and other parts of the cigarette lighter located below the receptacle unit 68.

Shown in FIG. 7 is a side view of another embodiment of the three tubed receptacle unit 68 with the length of the tubes in the range of 3.25 inches. This tube extends from the end 74 to the bottom 78 thereof which ends at the burner nozzle 50. Such a receptacle unit 68 may be attached to the commercial “Premixed 2” type nozzle shown in FIG. 3.

The flame stabilizer 76 is formed as a mesh structure from the titanium wire. The opening 82 is formed at the end 74 of the receptacle unit 68. The opening 82 coincides with the inside diameter of the inner tube 62 for insertion of the cigarette 70 into the receptacle unit 68. The opening 82 also serves as the exit for gases. As presented previously herein, this opening 82 is dimensioned in accordance with the common diameter of the filtered cigarettes. The burner used in the design of the cigarette lighter of the present invention is a known in the art as a Bunsen type burner.

The cigarette lighter 40 of the present invention having a design as shown in FIGS. 4-7 and described supra herein, was tested and the results of the tests which characterize the performance and safety features of the cigarette lighter were compared with the existing cigarette lighters, shown in FIGS. 1-3. The visible flame height, maximum heat flux, maximum center line temperature, and ultimately the maximum ignition height performance were all targeted in the cigarette lighter of the present invention and comparisons made with prior art cigarette lighters.

Practically, heat flux measurements are the strongest indicator for ignition propensity performance. Ignition time is dependent on incident heat flux, and material properties. The peak incident heat flux is an indicator of the various types of materials that may be ignited, while the heat flux vs. height profile indicates a region of the plume in which a particular material may be ignited. These two parameters may be used in comparison of ignition propensity performance of lighters.

The flame height HF is an important flame characteristic related to the lighter ignition propensity. The combustion chamber 52 of the cigarette lighter 40 of the present invention was designed to completely contain the flame. This resulted in a condition where there was no visible flame—which is a beneficial condition since the peak temperatures observed in the existing lighters of the prior art all occurred within the flame. Table 1 presents important nozzle physical characteristics. TABLE 1 Recession Fuel Injection Lighter Burner Flame Depth, Diameter Designation type Stabilizer δ_(light) (mm) (mm) Diffusion Port No 0 .5 Premixed 1 Bunsen Yes 6 .07 Premixed 2 Bunsen No 3 .07 Prototype Bunsen Yes 80 .07

The study of the subject lighter has been performed to compare its performance with existing cigarette lighters to characterize ignition propensity of all lighters and to prove that the lighter demonstrates an improvement in unwanted ignition propensity from a cigarette lighter without adding mechanical child safety features. An experimental facility was designed and constructed to characterize central line temperature, heat flux to a horizontal flat plane, and ignition of filter paper in order to investigate the ignition propensity of flames from these lighters. Diagnostics were employed to account for the scale of the experiment without sacrificing accuracy. The subject cigarette lighter has demonstrated improved ignition propensity over the existing cigarette lighters. TABLE 2 HAZARD CHARACTERISTICS FOR ALL NOZZLES TESTED. Visible Maximum Flame Maximum Maximum Ignition Lighter Height, Heat Flux, Temperature, Height Label H_(f)(mm) ({dot over (q)}₀ ^(″))_(max) (kW/m²) T_(max)(K) (h_(ig))_(max)(cm) Diffusion 20 63 1930.1 5.5 Premixed 1 9 169 1762.5 6.1 Premixed 2 15 326 2022.1 9.6 Prototype 0 51 1094.5 0

As seen in the Table 2, each nozzle produces a different flame height based on the geometry and type of combustion. In comparison with the prior art cigarette lighters only the cigarette lighter of the present invention produces no visible flame. The diffusion nozzle produces the longest flame height since the fuel-air mixing is limited by diffusion making the reaction zone longer. “Premixed 1” produces a dramatically shorter flame height because of the geometry of the burner, and corresponding fuel-air mixing. A portion of the flame exists within the combustion chamber, as illustrated in FIG. 2, and burned fuel reacts outside of the nozzle, greatly reducing the visible flame height measured from the lighter exit plane. “Premixed 2” produces a much longer flame height than “Premixed 1” because of its geometry. The “Premixed 2” nozzle creates a partially premixed flame with a fuel rich center. This partially premixed central core reacts more slowly than the well-mixed “Premixed 1” lighter, resulting in a longer reaction zone.

Temperature

Average center line temperatures were measured using a micro thermocouple and adjusted for radiation losses. The measured radiation corrected temperature for the cigarette lighter of the present invention illustrates significant near field improvement over the performance of the three existing nozzles. The maximum observed temperature for the subject lighter is approximately 1,095 K at h=2.0 mm. This is a temperature reduction of 928 K below the existing “Premixed 2” maximum temperature. Clearly, the amount of energy transferred to the combustion chamber 52 and flame stabilizer 76 show their significance in improving the hazardous performance of the lighter of the present invention.

While the near field temperature is greatly reduced, the far field temperature is not significantly reduced. This may result from a delayed turbulent transition compared to existing nozzles explained by a reduced effective energy release rate. This energy reduction is generally due to heat absorption by the combustion chamber and flame stabilizer. The reduction in the effective energy release rate causes a proportional reduction in critical Rayleigh number resulting in a delayed turbulent transition.

The diagram shown in FIG. 8, presenting a center line temperature of the tested lighters, indicates that the temperature of the cigarette lighter of the present invention near the exit plane 74, is much lower than those observed for the existing lighters (diffusion, “Premixed 1” and “Premixed 2”). Based on the data presented in FIG. 8, a scaling analysis can be performed for a comparison to existing data. The results of the scaling analysis performed are shown in FIG. 9 showing that turbulent plume behavior for the lighter of the present invention occurs at higher dimensionless height Z* than in the existing nozzles.

The scaling analysis for the lighter of the present invention resulted in the recession depth δ_(light)=approximately 79 mm since that is the height at which air can be freely entrained. A virtual origin was determined for the lighter of the present invention by matching the far field temperature decay to the (−5/3) power low decay observed for plumes. This method resulted in Z₀=85 mm which is conceptually correct since the flow propagating from a tube of the combustion chamber is not expected to behave as a plume initially.

The finite area of the tube and the finite velocity of the flow in the exit plane 74 dictates that entrainment does not follow plume behavior for some distance above the exit plane. According to the data in FIG. 9, fully established turbulent flow occurs at approximately Z*=6 which is greater than that of the existing nozzles. Temperature fluctuations also indicate a delay in the turbulent transition at approximately Z*=4 as illustrated in FIG. 10.

Surface Temperature

Surface temperatures are a significant factor in describing the performance and the commercial viability of a cigarette lighter. If the surface temperature of the lighter increases rapidly to the threshold of pain or even high enough to cause ignition of nearby materials, its unwanted ignition propensity performance will be suspect.

A simple heat transfer analysis was performed using a two-zone approach based on thermal resistance methods. A two-zone approach was used to account for the temperature difference along the length of each tube 62, 64 and 66, as illustrated by the data in FIGS. 11, 12, and 13. Each tube was split into two zones at the height of the flame stabilizer. The resistance analog was applied to the concentric radial tube configuration of the cigarette lighter.

The effects of radiation and natural convection were evaluated for each zone based on simple correlation using a first order approximation of Fourier's Law, Newton's Law of cooling, and the Stefan-Boltzmann Law presented by Incropera (Incropera F. B., et al., “Fundamentals of Heat and Mass Transfer”, 5^(th) Edition, John Wiley & Sons, New York, 2002). The model was also designed to resolve temperature performance after the nozzle was shut off. This was necessary to investigate the surface temperature increase of the outer tubes after the nozzle is shut off due to the continued heating from the inner tube 62.

In testing an uncooled cigarette lighter of the present invention, a natural cut-off time occurred regularly at 110 seconds. This natural cut-off time was the result of extreme heating and thermal expansion of the orifice such that the fuel flow was reduced to the point of extinction. Therefore, data was taken for the nozzle while the nozzle was shut off at time=110 seconds and the model prediction was calculated using the same cut-off time.

The results of the model temperature predictions are illustrated along surface temperature measurements taken with a similar shut-off time in FIGS. 11, 12, and 13 for each tube. The model illustrates reasonably accurate predictions of surface temperature for all tubes when the model inputs were set to known values for stainless steel. The key inputs for the model included the physical, thermal, and geometric properties for all three tubes, a shut off time, a time step, the total energy release rate of the flame, and an approximation of the fraction of energy transferred from the flame to the inner tube 62.

This model can be also used in predicting surface temperature performance differences when the construction material properties are changed. Sensitivity analysis of the model for designs of similar geometry shows that material with high density, high specific heat, and low emissivity, illustrate improved performance. Polished stainless steel appears to have been a good selection of material for the tubes 62, 64, and 66 due to the fact that it has a high density, high specific heat, and low emissivity. The three tube configuration also demonstrates a dramatic surface temperature improvement over the two tube configuration.

The peak exposed surface temperature of the lighter of the present invention also has better performance in comparison to that of “Premixed 1” for similar operation time, as illustrated in FIG. 14. The peak exposed temperature of the subject lighter is 344K at T=379.5S and the peak exposed temperature for “Premixed 1” is 453K at T=110 seconds. In fact, the performance of the middle tube 64 is better than “Premixed 1”. Depending on the level of safety desired, a two tube design may be determined as sufficiently safe.

Heat Flux

The heat flux measurements for the cigarette lighter of the present invention demonstrate an improvement over existing nozzles. The maximum observed heat flux was 51 kw/m² at h=2 mm, as shown in Table 2. The radial heat flux profile corresponding to the peak observed heat flux for all of the lighters is illustrated in FIG. 14. The stagnation point heat flux vs. height is illustrated in FIG. 15 for the lighter of the present invention compared to the lighters of the prior art (diffusion, “Premixed 1”, and “Premixed 2”). The data for the subject lighter is indicative of the worst case scenario. In actual use, one designation propensity performance will be lower than the values reported for nearly all instances of operation.

Unwanted Ignition

An ignition test was designed in a simple configuration to evaluate the unwanted ignition propensity in a controlled environment. A thin sheet of filter paper was placed horizontally above the lighter. As the result of several ignition test trials with the lighter of the present invention, no flaming ignition was observed. Only a few tests resulted in any visible smoldering of the filter paper, while many tests of the same height illustrated no visible ignition. Therefore, ignition testing of the subject lighter illustrated no significant ignition time. The studies performed have shown that the cigarette lighter of the present invention was designed following the concept of a combustion chamber into which a cigarette would be inserted for ignition.

The flame stabilizer is needed in this design to limit the insertion of the cigarette since inserting of the cigarette too close to the source of flame may cause extinction of the flame. The combustion chamber in combination with flame stabilizer also acts as a heat sink for the flame. The subject lighter uses three concentric stainless steel tubes with the inside diameter of the inner tube approximately 9.65 mm slightly greater than the diameter of the cigarette. Three tubes were selected since the outer tubes act as a radiation shield for the inner tube, effectively increasing the time over which the energy absorbed is released to the environment. The flame recession concept was successful in reducing all of the unwanted ignition hazard characteristics as was illustrated by data presented in Table 2.

A simple comparison of the critical hazard parameters describing ignition propensity illustrates that the cigarette lighter of the present invention successfully improves unwanted ignition propensity performance when compared to existing cigarette lighter designs. The data related to the novel cigarette lighter demonstrates significant reduction in flame height, peak central line temperature, maximum observed incident heat flux, and critical ignition region.

Such performance improvements include: (1) visible flame height is reduced to zero, (2) peak central line temperature is reduced by 836K, 668K, and 928K in comparison with diffusion, “Premixed 1”, and “Premixed 2” types of the lighters, (3) maximum observed heat flux is reduced by a factor of 1.24, 3.23, and 6.42 from the diffusion, “Premixed 1”, and “Premixed 2” types of the lighters, respectively, and, (4) critical ignition height for filter paper is reduced effectively to zero based on ignition tests. The performance caveat of the subject cigarette lighter is the exposed surface temperature of the nozzle at the exit end 74 of the lighter. This caveat can be resolved by selecting materials with high density, high specific heat, and low surface emissivity as well as by increasing the number of concentric tube in the design. The design selected illustrates lower exposed surface temperature than those observed for example, “Premixed 1” type cigarette lighter demonstrating an acceptable performance level for commercial viability. The novel lighter also has sufficient heating capacity to ignite a cigarette when the cigarette is inserted into the combustion chamber towards the flame stabilizer. Overall, the novel cigarette lighter illustrates an effective concept and design in reducing the unwanted ignition propensity of cigarette lighters without introducing mechanical child safety features.

Although the invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the invention as defined in the appended claims. For example, equivalent elements may be substituted for those specifically shown and described, certain features may be used independently of other features, and in certain cases, particular locations of elements may be reversed or interposed, all without departing from the spirit or scope of the invention as defined in the appended claims. 

1. A cigarette lighter with improved safety properties, comprising: a combustion chamber, a burner nozzle coupled to said combustion chamber to deliver a fuel-air mixture thereto, and an ignition unit operatively coupled to said combustion chamber to ignite said fuel-air mixture therein to produce a flame, said combustion chamber including a receptacle unit sized to completely contain therein said flame produced in said combustion chamber.
 2. The cigarette lighter of claim 1, wherein said receptacle unit has an opening to receive therethrough a cigarette to be lit, said opening having dimensions on the order of substantially the diameter of a cigarette.
 3. The cigarette lighter of claim 1, wherein said receptacle unit includes a plurality of concentric tubes.
 4. The cigarette lighter of claim 3, wherein said concentric tubes are vented tubes, each tube having openings formed at predetermined locations thereof.
 5. The cigarette lighter of claim 1, further comprising a flame stabilizer positioned within said receptacle unit.
 6. The cigarette lighter of claim 1, wherein the length of said receptacle unit is on the order or exceeds approximately 3.25″.
 7. The cigarette lighter of claim 3, wherein said plurality of concentric tubes includes an inner tube, an outer tube, and a middle tube concentrically sandwiched between said inner and outer tubes, said inner tube having an inner diameter not exceeding approximately 0.38″.
 8. The cigarette lighter of claim 1, further comprising: a fuel reservoir, containing a fuel, an air-fuel mixing chamber coupled to said fuel reservoir through a fuel connection tube, said air-fuel mixing chamber being coupled to said burner nozzle to inject therethrough said fuel-air mixture into said combustion chamber; and an operation button; wherein said ignition unit includes a piezoelectric spark device actuated by said operation button, and a spark ignition wire extending between said spark device and said combustion chamber.
 9. A cigarette lighter with improved safety properties, comprising: a combustion chamber, a burner nozzle coupled to said combustion chamber to deliver a fuel-air mixture thereto, and an ignition unit operatively coupled to said combustion chamber to ignite said fuel-air mixture therein to produce a flame therein, said combustion chamber including a receptacle unit formed from a plurality of concentric vented tubes.
 10. The cigarette lighter of claim 9, wherein said plurality of concentric vented tubes includes: a first tube having an outer diameter, and a second tube having an inner diameter and an outer diameter, said inner diameter of said second tube being greater than said outer diameter of said first tube.
 11. The cigarette lighter of claim 10, wherein said vented tubes further include a third tube having an inner diameter greater than said outer diameter of said second tube, said second tube being concentrically sandwiched between said first and third tubes.
 12. The cigarette lighter of claim 9, wherein said concentric tube are formed of stainless steel.
 13. The cigarette lighter of claim 11, wherein said first tube has an inside diameter not exceeding the diameter of a cigarette to be lit by said flame produced in said cigarette lighter.
 14. The cigarette lighter of claim 9, wherein the length of said vented tubes exceeds the length of said flame, said flame being completely contained in said receptacle unit.
 15. The cigarette lighter of claim 11, wherein said concentric vented tubes have a plurality of ventilation openings formed in said tubes, said ventilation openings being arranged in a predetermined fashion one with respect to another.
 16. The cigarette lighter of claim 15, wherein said ventilation openings of said first and second tubes include circularly shaped openings having a diameter ranging about 3.2 mm.
 17. The cigarette lighter of claim 15, wherein said ventilation openings of said third tube include circularly shaped openings having a diameter ranging about 4.8 mm.
 18. The cigarette lighter of claim 11, further comprising a flame stabilizer positioned inside said first tube a predetermined distance from said burner nozzle.
 19. The cigarette lighter of claim 18, wherein said flame stabilizer includes a mesh structure made of titanium wire.
 20. The cigarette lighter of claim 9, further comprising: a fuel reservoir containing a fuel, an air-fuel mixing chamber coupled to said fuel reservoir, said air-fuel mixing chamber being coupled to said burner nozzle to inject therethrough said fuel-air mixture into said combustion chamber; and an operation button, operatively coupled to said ignition unit to actuate the same to produce the flame in said combustion chamber. 